Fungi contain a group of phosphoinositol containing sphingolipids not found in higher animals. These lipids provide a logical focus for the rational design of antifungal agents for use in alleviating human fungal infections. The long term objectives of the proposed research with S. cerevisiae is to define in some detail the metabolic pathways associated with the synthesis and degradation of these lipids and to define the biological function(s) of these compounds. Recently developed high resolution separation methods will be applied to in vivo pulse-chase studies of the incorporation and turnover of radioactive precursors into the phosphosphingolipids of yeast. Individual synthetic steps will be studied in vitro with enzyme preparations derived from yeast membranes. A group of recently isolated yeast mutants that require a long chain base for growth will be employed to define the genes responsible for this auxotrophy and to define the role of each gene in sphingolipid metabolism. These mutants will also be studied as long chain base starvation progresses to discover changes in normal biochemical processes that may give insight into the function(s) of sphingolipids.